The present invention concerns a timepiece power reserve indicator device, i.e. a device allowing the degree of development or winding of the mainspring of a mechanical timepiece to be indicated to the wearer.
Timepiece power reserve indicator devices such as that described in Swiss Patent No. CH 689 414 are already known. This indicator includes an operating pinion which is secured to the hour wheel and whose staff constitutes the staff of a plane differential gear. Said operating pinion drives a satellite pinion which pivots on a plate and which meshes with the inner toothing of a differential crown. This differential crown, which is freely fitted onto a cylindrical core of the plate, includes an outer toothing which meshes with a power reserve pinion secured to the barrel arbour.
When the hour wheel rotates, it drives the operating pinion which meshes with the satellite pinion. Since the differential crown is substantially stationary during the normal working of the watch, the satellite pinion rotates on itself about its axis and rolls on the inner toothing of said differential crown, which causes the plate to rotate. The plate itself carries an indicator disc which makes an angular movement as a function of the reserve of power which can still be assured by the winding of the mainspring.
Conversely, when the mainspring is wound, the hour wheel, and thus the operating pinion, remain substantially stationary. However, the barrel arbour on which a pinion is mounted, rotates. By rotating, this barrel arbour pinion drives the differential crown via an intermediate wheel. In turn, the differential crown meshes with the satellite via its inner toothing. Since the hour wheel is stationary, the satellite rolls on the operating pinion and drives the plate in rotation. The indicator disc, carried by the plate, makes an angular movement in the opposite direction to the previous one as a function of the power reserve assured by the number of winding turns of the mainspring.
The power reserve indicator mechanism described above has serious drawbacks. When the hands of the watch are being set, this mechanism has to be blocked to prevent the power reserve indication being made incorrect by the rotation of the hour wheel onto which the operating pinion is secured. In order to overcome this problem, Swiss Patent No. CH 689 414 proposes a rather complex system wherein the power reserve indicator disc is fitted elastically onto the plate. A hand-setting spring moves under the action of the hand-setting stem and acts onto a limitation stud which compresses the indicator disc against the frame, so that said indicator disc is no longer driven by the plate and remains stationary in the position which it occupies. A construction of this type, including several parts in movement with respect to each other, is unreliable and easily able to be damaged.
The object of the present invention is to overcome the above problems and drawbacks in addition to others by providing a timepiece power reserve indicator device which is compact and of very simple design.
The present invention therefore concerns a power reserve indicator device for a manually or automatically wound timepiece, said timepiece including a barrel, a mainspring housed in the barrel and time display elements mechanically coupled to said barrel, said indicator device including a differential gear a first input of which is driven by a winding gear train which meshes with a first driving gear formed by the barrel core, the output of said differential gear driving a display gear train for indicating the reserve of power assured by the number of winding turns of the mainspring, characterised in that the second input of the differential gear is driven by a letting down gear train which meshes with a second driving gear formed by the outer toothing of said barrel or by a wheel and pinion driven by said barrel.
As a result of these features, the present invention provides a power reserve indicator device including distinct winding and letting down gear trains, so that this device can easily be integrated in a large number of different watch movements.
According to a complementary feature of the invention, the differential gear is positioned at the centre of the movement, on the hour wheel. This allows the power reserve display to be distributed indifferently over all the positions of the dial, and the differential gear to be arranged inside the date disc. Moreover, if the differential gear was not positioned at the centre of the movement, it would have to be smaller, and would thus be more difficult to make.
According to another feature of the invention, the differential gear is of the simple planetary type whereas usually the differential gears used in power reserve indicator mechanisms are of the double satellite and double central pinion planetary type. This solution thus allows a flatter differential gear to be obtained than in the past, which substantially reduces the bulkiness thereof.